Apparatus for cooling and calibrating extruded plastic profiles

ABSTRACT

The invention relates to an apparatus for cooling and calibrating extruded plastic profiles with a trough which is provided downstream of a dry calibrating device and has a water bath through which the profile is guided, with plates being arranged in the trough between the face walls in order to calibrate the profile under the influence of negative pressure. In order to achieve a high production speed with a low amount of expenditure it is proposed that a sleeve encompassing the profile is provided in a section of the trough, which sleeve guides at least in a zone of the main body of the profile and that the sleeve is provided with a distance to the face walls in the longitudinal direction.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for the cooling andcalibration of extruded plastic profiles with a trough which is provideddownstream of a dry calibrating device and comprises a water baththrough which the profile is guided, with apertures being arranged inthe trough between the face walls for calibrating the profile.

An installation for the production of plastic profiles as are used forthe production of windows or doors usually currently comprises thefollowing arrangement: An extruder produces a profile of doughyconsistency made of plastic granulate. One or several dry calibratingdevices will cool the profile to a certain extent, so that a somewhatstable form is achieved. Dry calibration substantially consists of asteel block with an opening through which the profile is guided and witha plurality of vacuum slots in order to suck the profile under pressureagainst the walls of the opening. In this way the collapse of the stillsoft profile is prevented. Furthermore, several cooling ducts areprovided. One or several wet calibrating apparatuses will ensure thefinal cooling and shaping of the profile. Wet calibrating apparatusesaccording to the so-called swirl bath principle have proven to beparticularly beneficial in the past few years. In such apparatuses thetrough is subdivided by calibration plates into several chambers and aturbulent flow of the cooling medium in the trough is caused by openingsin the plates. A negative pressure present in the trough will press theprofile against the calibration plates. This allows for a precisecalibration and rapid cooling of the profile with a lower waterconsumption. A caterpillar pull-off will draw the profile through theupstream calibrating devices.

The technical progress of extruders and the recipes for profileextrusion has led to continuously rising demands placed on the workspeed of extrusion lines. In order to meet these demands it is currentlycommon practice to arrange several dry calibrations behind one anotherand, downstream of the same, to provide one or several water baths. Drycalibrations are very costly, however, so that for cost reasons areduction in their number would be desirable.

Calibration systems can be used for slow working extrusion lines whichmake do with only one single dry calibration with the common length ofapprox. 300 mm. If in such a system the work speed is increased over arelatively moderate value, high-quality profiles can no longer beproduced.

DESCRIPTION OF THE PRIOR ART

From DE 27 40 989 A, a calibration device for plastic profiles is knownin which a profile is calibrated and cooled under vacuum in a waterbath. A pipe element is attached to the entry-sided face wall of thecalibrating trough in order to guide and calibrate the profile after theentry over a certain distance. However, there are unclear pressuresituations in the interior of this pipe, so that a close fit of theprofile on the tube is not ensured. In particular, the wetting with thecooling water in the space between the profile and the sleeve is notensured.

Moreover, from DE 27 34 831 A, an extrusion apparatus for pipes is knownin which a water bath is provided immediately downstream of a drycalibration apparatus, which water bath is arranged as in theaforementioned specification. It substantially also has the samedisadvantages.

SUMMARY OF THE INVENTION

It is the object of the present invention to avoid such disadvantagesand, on the one hand, to achieve high production speeds by achieving, onthe other hand, a reduction of the required expenditure. In particular,the present invention is to allow making do with only one single drycalibration of the usual length.

These objects are achieved in accordance with the invention that atleast one sleeve encompassing the profile is provided in a section ofthe trough, which sleeve guides at least one zone of the main body ofthe profile and, that a gap between the profile and the sleeve is inconnection with the water bath on either side. Preferably, the sleeve isprovided in the longitudinal direction with a distance to the facewalls.

It was established that a main cause of the inadequate profile qualityin the case of reducing the number of dry calibration apparatuses isthat the profiles enter the water bath in a still very hot and thereforesoft state. As a result of the negative pressure which prevails by thesystem in such a wet calibration, the profile is pulled apart in thezones between the calibration apertures, as a result of which innerbridges of the profiles are expanded in an uncontrolled manner. Althoughthe outer contour of the profile is finally brought back again to thedesired shape by the calibration apertures, the inner bridges of theprofiles are beyond repair. Such profiles can no longer be used inpractice.

In the present invention the profile is protected in a first section ofthe water bath from the attack of the vacuum by the sleeve. As theforces by the vacuum are proportional to the surface area on which theyact, a guidance of the profile is mainly required in the zone of themain body.

The relevant aspect in the invention is that the sleeve is in connectionwith the cooling water at least at either end. This is achieved mosteasily in such a way that the sleeve is provided at its face sides witha distance to adjacent components such as the face wall of the trough.Apertures in the sleeve can also be provided which secure a continualwetting of the gap between profile and sleeve.

It is particularly favourable if the length of the sleeve is between 100and 400 mm, preferably between 250 and 320 mm. Particularly in the casewhen the sleeve is provided with a thin-walled arrangement a furtherrapid cooling of the profile is achieved by the cooling medium flowingin the outer zone of the sleeve, so that downstream of the sleeve theshape has already stabilised to such an extent that there is no dangerof any over-extension of the inner bridges of the profile.

In a particularly favourable embodiment of the invention, a guidance isprovided in particular in the zones of the connection of the innerbridges with the outer shape of the profile. In this way theparticularly critical parts of the profile are reliably protected.

Preferably, the sleeve is arranged in an upstream area of the trough.Several sleeves can also be provided behind one another. A particularlyreliable cooling without endangering the shape of the profile can beachieved in this way with simple means.

It is particularly favourable if the sleeve is held by several platesand if the plates subdivide the trough into chambers in the axialdirection of the profile, with apertures being provided in the zone ofthe sleeves to allow cooling medium to flow through. It can be providedin particular that at one end of the trough there is provided an inletopening for a cooling medium and at the other end of the trough anoutlet opening for a cooling medium, so that the trough is substantiallyflowed through by a cooling medium in the longitudinal direction. Anoutstanding cooling effect can be achieved by this solution with a lowwater consumption.

A particularly simple arrangement of the apparatus in accordance withthe invention can be achieved that preferably the sleeve and/or thecalibration plates are held movable in a limited manner in one directiontransversally to the axial direction of the profile. A complexadjustment of the sleeve and the calibration plates transversally to theaxial direction of the profile can thus be omitted. Tensions and aclamping effect, owing to an insufficient adjustment, can thus besecurely prevented.

The present invention further relates to a system for the cooling andcalibration of extruded plastic profiles with a dry calibration in whichthe extruded profile is cooled and calibrated by the application ofvacuum. In this process one or several troughs are optionally used inwhich calibration plates are arranged in a water bath.

A particularly precise adjustability and fine-tuning capacity of thecalibration is enabled in such a way that a trough equipped with atleast one sleeve is provided downstream with a further trough withcalibration plates in which there is a lower negative pressure than inthe first trough.

It has been seen further that the vacuum in the dry calibration devicecan be maintained in a particularly favourable manner in that the troughis directly flanged onto the downstream face side of the dry calibratingdevice, so that the same is directly in contact with the cooling medium.As a result of this embodiment, the power demand of the vacuum pump forthe dry calibration is kept low and a stability of the achieved vacuumis reached which has a positive effect on the profile quality.

As a result of the system in accordance with the invention, existingproduction lines with only one dry calibrating unit can be operated withsubstantially higher production speeds.

The achievement of the highest possible extrusion speeds is possible inhigh-performance systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in closer detail by reference to theembodiments represented in the drawings, wherein:

FIG. 1 schematically shows an extrusion line with an apparatus inaccordance with the invention;

FIG. 2 shows an apparatus in accordance with the invention in a sideview on an enlarged scale;

FIG. 3 shows a sectional view according to line III—III in FIG. 2 on anenlarged scale and FIGS. 4 to 6 show altered embodiments in sectionalviews according to that of FIG. 3.

In the description of the figures, components with a principally similarfunction are designated in the individual embodiments with the samereference numerals, even if their shape is different.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The extrusion line of FIG. 1 consists of the following components whichare arranged successively behind one another: an extruder 1, a drycalibrating device 2, a wet calibrating device 3 and a caterpillarpull-off 4. The wet calibrating device 3 consists of a trough 5 which isflanged directly onto the face wall 6 of the dry calibrating device 2and which is occluded towards the caterpillar pull-off by a downstreamface wall 7. In the upstream zone, cooling water is supplied through acooling water connection 8, whereas at the other end of the trough 5 thecooling water is discharged from the trough 5 by way of a furthercooling water connection 9. A negative pressure is produced in theinterior of the trough 5 by way of a vacuum connection 10. In theupstream region of trough 5 a sleeve 11 is arranged which is held by twofixing devices 12, 13. Sleeve 11 is slightly distanced from face wall 6.The length 1 of sleeve 11 is 300 mm, like that of the dry calibratingdevice 2. Calibrating plates 14, 15, 16 are provided downstream ofsleeve 11, which plates calibrate the profile 17 in the known manner.Apertures 18 in the plates 14, 15, 16 are used for producing a turbulentflow of the cooling water, as is described in the European Patent No. 0659 536.

FIG. 2 shows a slightly altered embodiment of the present invention onan enlarged scale. In the embodiment of FIG. 2 the trough 5 is occludedat the upstream end by an own face wall 6 a. Two sleeves 11 a, 11 b arearranged behind one another in trough 5. The sleeves 11 a, 11 b are heldby plates 12 a, 13 a and 12 b, 13 b, respectively. The distances xbetween the face wall 6 and the first sleeve 11 a or the distances ybetween the first sleeve 11 a and the second sleeve 11 b aresufficiently small with a few millimeters in order to prevent anydeformation of the profile as a result of the negative pressure intrough 5.

A further trough 5 a is connected on the downstream end of the trough 5in accordance with the invention, which further trough is arranged inthe common manner as a water bath, as is described in the EuropeanPatent No. 0 659 536. Said further trough 5 a is not subjected to such ahigh negative pressure as the first trough 5. Depending on theproperties of the profile and the other boundary conditions of thecalibration, the first trough is set approximately to an absolutepressure of 0.4 to 0.7 bars, whereas a pressure of between 0.6 to 0.8bars is set in the second trough 5 a. Here, the absolute pressure in thesecond trough 5 a is approx. 0.1 to 0.2 bars higher than in the firsttrough 5.

The embodiment of FIG. 2 is also distinguished from the embodiment ofFIG. 1 in that the cooling water is sucked in by way of a first inletopening 8 a. No pump is provided in the zone of said first inlet opening8 a and the negative pressure in trough 5 is used exclusively to causethe inflow. The cooling water stream can be set by way of a regulatingapparatus which is not shown. At the downstream side at the end of thetrough a second connection 10 a is provided which is connected with aregenerative water pump which is not shown here. On the one hand, therequired vacuum in trough 5 is produced by way of said connection 10 aand, on the other hand, the cooling medium is drawn off. As a result ofthis design, a strong negative pressure can be produced in trough 5 withrelatively simple means. In summary, it is possible by the presentinvention to achieve an improved profile quality by a strongerevacuation of trough 5 because the profile 17 is pressed more stronglyagainst the sleeves 11 a, 11 b and the calibration plates 14, 15, 16.

In the embodiment of FIG. 3, the profile 17 is completely encompassed bysleeve 11. Sleeve 11 consists of the individual components 21, 22, 23and 24 which are screwed together. Sleeve 11 of FIG. 3 is heldfloatingly in plates, of which plate 13 a is visible in FIG. 3. As aresult of this arrangement, the precise position of sleeve 11 isdetermined by the profile 17, so that an arrangement with precise truealignment of all plates is not required in the production of theapparatus in accordance with the invention. As a result of the slightmobility of sleeve 11 in plate 13 a, any slight imprecisions can becompensated without causing any danger of unnecessary deformation of theprofile 17 or any jamming. A plurality of recesses 25 is providedbetween the sleeve 11 which cause a turbulent flow of the cooling waterdirectly on the outer side of the sleeve 11. A particularly intensivecooling of the sleeve 11 is achieved in this way.

The embodiment of FIG. 4 corresponds substantially to the one of FIG. 3with the difference that the plate is composed of four single parts 33a, 33 b, 33 c and 33 d so as to allow an installation of the sleeve 11from above. The sleeve 11 with its individual components 21, 22, 23 and24 is not screwed together in this embodiment, but is held together bythe plate 33 a to 33 d. A floating mounting is naturally not possible inthe vertical direction in this embodiment. Projections 31 in the plateelement 33 a and 32 in the plate element 33 d hold the sleeve 11 in avertically precisely defined position and press the individual parts 21to 24 of sleeve 11.

The individual parts 21 to 24 of sleeve 11 are also held together by theplate sections 33 a, 33 b, 33 c and 33 d in the embodiment of FIG. 5.The difference in this embodiment is that the sleeve 11 does notcompletely encompass the profile 17. A first profile projection 17 aprojects freely upwardly from the sleeve 11. A second profile projection17 b is enclosed with a distance by sleeve 11. Lining grooves 17 c, 17 dand 17 e are placed freely in the inner zone and a free placement isalso provided in a corner zone 17 f of the profile 17, i.e. a gapbetween sleeve 11 and profile 17. In this way the friction betweenprofile 17 and the sleeve 11 can be reduced without impairing theefficiency of the present invention. The relevant aspect is that thelarge-surface wall areas of profile 17 are securely supported by sleeve11.

FIG. 6 shows a particularly simple embodiment of the invention which issuitable for small profile cross sections. The inner profile of sleeve11, which is composed of two components 21 and 22, is eroded into acylindrical blank. The embodiment of FIG. 6 is arranged in such a waythat sleeve 11 is rigidly connected with the lower plate section 33 a,with the two parts 11 a and 11 b of the sleeve 11 being tightly screwedtogether. It is obvious for the man skilled in the art that thiscylindrical sleeve 11 can also be held floatingly.

The present invention allows the highest possible production speed at anextremely inexpensive arrangement of an extrusion line. Already existingtools can be retrofitted in a simple manner in order to achieve aconsiderably increased production output. As no slots or apertures areprovided in the sleeves transversally to the direction of production, ahigh surface quality is achieved.

Furthermore, an extremely low friction is achieved by a water filmbetween profile and sleeve, which ensures a very low shrinkage. Alltold, it is possible by the present invention to combine the function ofa dry calibration with the simplicity of a swirl bath and to achievewith simple means the highest production output at good quality.

What is claimed is:
 1. An apparatus for cooling and calibrating extrudedplastic profiles with a trough having face walls and which is provideddownstream of a dry calibrating device and comprises a water baththrough which the profile is guided, with calibrating plates having aplurality of apertures therein and being arranged in the trough betweenthe face walls in order to calibrate the profile under the influence ofnegative pressure, said plurality of apertures create turbulance withinsaid trough, wherein a sleeve encompassing the profile is provided in asection of the trough, which the sleeve guides at least a portion of themain body of the profile and that a gap between the profile and thesleeve is in connection with the water bath on either side of thesleeve, and wherein the sleeve is held by several plates, the platessubdivide the trough into chambers in the axial direction of theprofile, with openings being provided in the zone of the sleeve forallowing the cooling medium to flow through.
 2. An apparatus accordingto claim 1, wherein the sleeve is provided in the longitudinal directionof the trough with a distance to the face walls.
 3. An apparatusaccording to claim 1, wherein the length of the sleeve is between 100and 400 mm.
 4. An apparatus according to claim 1, wherein the length ofthe sleeve is between 250 and 320 mm.
 5. An apparatus according to claim1, wherein the sleeve has a wall thickness of between 5 and 10 mm.
 6. Anapparatus according to claim 1, wherein said sleeve provides furtherguidance in the zones of the connection of inner bridges with the outercontour of the profile.
 7. An apparatus according to claim 1, whereinthe sleeve is arranged in an upstream zone of the trough.
 8. Anapparatus according to claim 1, wherein several sleeves are arrangedsuccessively behind one in the trough.
 9. An apparatus according toclaim 1, wherein an inlet opening for a cooling medium is provided atthe one end of the trough and a discharge opening for a cooling mediumis provided at the other end of the trough, so that the trough issubstantially flowed through in the longitudinal direction by a coolingmedium.
 10. An apparatus according to claim 1, wherein the sleeve or thecalibrating plates are held movable in one direction transversely to theaxial direction of the profile.
 11. An apparatus according to claim 1,wherein the sleeve completely encloses the profile.
 12. An apparatusaccording to claim 1, wherein in the trough there are provided a firstconnection for sucking in cooling water and a second connection forsucking in air and cooling water, with a regenerative water pump beingconnected to the second connection which in addition to the circulationof the cooling water also produces the required vacuum in the trough.